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It's not reasonable to expect people to download a 1.3 GB file and try to load it into Wireshark in order to tell you what's happening with seven packets. Cut the capture file down to a more reasonable size. To save packets 700 to 900, for example, you could enter a display filter of "frame.number > 699 && frame.number < 901". You can then go to File > Export Specified Packets to save off only the displayed packets.

1 Answer

Always consider the point you're capturing on. You trace has strong signs of being captured on the sender itself.

Therefore:

Q1) As you're on the server itself, you just don't see ACKs because they had not come to you at the moment and still are somewhere on the path. It seems the sender has congestion window big enough to transmit packets 16...22 without waiting for an ACK.

Q2) This is because of "TCP segmentation offload". Please watch Paul Offord's cool video to grasp the concept: